Lone Wolf claims that you don't have to change any other part, other than mags for their .40 to 9mm conversion barrels. KKM conversions are supposedly the same way.
I have no experience with either for 40-9.
That is correct.
I have a G27 with the Lone Wolf 9mm conversion barrel. The only thing I changed was the barrel and the magazines. I have never had a jam using the conversion barrel and in fact it is more accurate than the stock .40 barrel.
I got the 2 port extended barrel. I use it so I can shoot the cheaper 9mm at the range. I always carry with it "factory" original.